Effect of non-toxic corrosion inhibitors on steel in chloride solution

International audienceThe effect of certain non-toxic inhibitors on the corrosion resistance of ordinary steel in chloride solution (2 × 10−2 M NaCl) at pH 8 was studied by polarisation curves, Raman spectroscopy and the electrochemical quartz crystal microbalance (EQCM).The inhibitors tested were ascorbic acid salts (SA) and 1-hydroxyethylidene, 1-diphosphonic acid salts (SHEDP), the results from addition inhibtors are carried in order to expect a combined effect.The polarisation curves indicated an improvement in polarisation resistance with the addition of SA or SHEDP alone. In the presence of (SA + SHEDP), the inhibiting effect were further improved. Raman spectroscopy analyses confirmed the presence of a film formed by the two inhibitors at the iron electrode surface.The individual behaviour of each inhibiteur was studied with EQCM for different chloride concentrations. The maximum of mass variation was obtained for a lower concentration in the case of SHEDP. The adsorption coverage was calculated. The Langmuir-Freundlich isotherm model is used to fit adsorption of the inhibitors. Interactions between adsorbed species were detected for SHEDP case.For inhibitor mixture, detected mass attained plateau for low(er) inhibitors concentration mixture. At higher concentration, the mass quantity was smaller than that calculated from the sum of detected mass for each alone coumpound. However it provided better protection